INSTITUTO DE FISICA LA PLATA
Unidad Ejecutora - UE
congresos y reuniones científicas
XAFS AND SAXS STUDIES OF THE INTERACTION OF DIFFERENT CAPPING POLYMERS WITH PLATINUM NANOPARTICLES
KOEBEL, M. M.; REQUEJO, F. G.; CRAIEVICH, A. F.; RAMALLO-LÓPEZ, J. M.; GIOVANETTI, L.; FOXE, M.; JONES, L.; SOMORJAI, G. A.
Congreso; 5th Brasilian MRS Meeting; 2006
Pt nanoparticles (NP) were synthesized by seeded growth and direct ethylene glycol reduction methods and stabilized with two different polymers: poly-(vinylpyrrolidone) (PVP) and sodium polyacrylate (PAA-Na). The shape and size distribution of the NP was determined using transmission electron microscopy (TEM). Complementary, small angle X-ray scattering (SAXS) experiments were performed to estimate the average NP size and size distribution. In addition, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies were performed to elucidate the effect of the capping agent on both shape/geometry and electronic structure of the NP. SAXS and TEM measurements corroborate the sharp and well defined size and shape distribution on each set of NP. While the PVP capping seems to interact only weakly with the Pt atoms on the NP surface, the PAA-Na capping causes significant changes in the electronic structure of the NP surface and adds new contributions to the atomic radial distribution function of Pt atoms as determined by EXAFS. This stronger interaction with the charged polyacrylate groups or sodium ions could also be responsible for the change in the Pt 5d electronic configuration observed by XANES. Two different mechanisms for adsorption of the polymer to the Pt NP surface are proposed. The combination of TEM, SAXS, EXAFS and XANES techniques allows one to characterize structural and electronic changes in noble metal NP with different types of capping agents. Acknowledgements: We would like to acknowledge the financial support received from projects PICT 06-17492 (ANPCyT, Argentina), PIP 6075 (CONICET, Argentina), CIAM collaborative project (CONICET, NSF and CNPQ), D04B - XAS1 4246/05, D11A - SAXS1 4719/05 (LNLS, Brazil), Lawrence Berkeley Nationanal Laboratory Materials Science Division, the University of California,Berkeley and the Swiss National Science foundation.